Tool positioning system

ABSTRACT

Apparatus for positioning and holding a tool ( 3 ) relative to a workpiece ( 35 ) comprising a carriage ( 1 ) for conveying the tool over the surface of the workpiece ( 35 ) and means ( 7, 9, 11, 13 ) for holding the carriage ( 1 ) onto the surface of the workpiece ( 35 ), the holding means being selectively switchable between a low grip state in which the carriage ( 1 ) is held against the workpiece surface whilst remaining capable of movement relative thereto and a high grip state in which the carriage ( 1 ) is held substantially fixedly to the workpiece surface for the tool ( 3 ) in use to operate thereon. Such an arrangement provides a robot capable of “crawling” over a workpiece ( 35 ) and carrying out precise manufacturing operations thereon.

This application is the US national phase of international applicationPCT//GB01/02994 filed 4 Jul. 2001 which designated the U.S.

This invention relates to the positioning and holding of a tool relativeto a workpiece on which the tool is intended to carry out one or moreoperations, and is particularly but not exclusively related tomanufacturing.

In manufacturing industry it is common to carry out such manufacturingoperations on workpieces as measuring, drilling, milling, cutting,countersinking and inspecting; tools for such operations are well knownin the art and form no part of the present invention per se, however theterms “tool” and “tools” as used hereinafter should be understood toembrace all such apparatus for performing any such operation.

The accuracy with which such tools are positioned is dependent upon thelevel of accuracy required in the finished product. In applications inwhich a high degree of accuracy is required, such as the aircraftindustry, a significant proportion of the manufacturing time and cost isaccounted for by the need to ensure that tools are accurately positionedrelative to the workpiece in order that a number of manufacturingoperations can be performed with accuracy and at precisely definedlocations on the surface of the workpiece. In conventionalmanufacturing, tools are located by hand with the assistance of jigs andfixtures, which are costly and complicated items in themselves.Alternatively, tools may be located by robot arms, however such methodsare costly and inherently inaccurate, particularly where the workpieceis large and requires successive tool operations to be carried out overa large area.

Accordingly, the present invention provides an apparatus for positioningand holding a tool relative to a workpiece comprising a carriage forconveying the tool over the surface of the workpiece and means forholding the carriage onto the surface of the workpiece, the holdingmeans being selectively switchable between a low grip state in which thecarriage is held against the workpiece surface whilst remaining capableof movement relative thereto and a high grip state in which the carriageis held substantially fixedly to the workpiece surface for the tool inuse to operate thereon.

Such an arrangement enables a manufacturing tool to be moved over thesurface of a workpiece between precisely predetermined positions thereonin order to perform the desired manufacturing operations whilstmaintaining the necessary level of accuracy; the carriage simply movesthe tool to the location on the workpiece where the next operation is tobe carried out, and the holding means switch to the high grip state soas to hold the tool in a fixed spatial relationship with the workpiecesurface so that the desired manufacturing operation can be accuratelyperformed. As will be appreciated such apparatus can be designed so asto be compact and relatively inexpensive when compared with the cost oftraditional jig-based tool positioning methods. Moreover, more than onesuch apparatus may be used on a workpiece at one time, something notnormally possible with traditional techniques, thus reducingmanufacturing times.

The function of the holding means in the low grip state is to hold thecarriage against the workpiece whilst it is moving, and the tool is notperforming a manufacturing operation, so that the apparatus can “roam”over the entire surface of the workpiece, whether that surface be at asteep angle, or even inverted, without becoming detached from thesurface. Clearly the attractive force exerted by the holding means tohold the carriage onto the workpiece surface in the low grip state mustbe approximately equal to the overall weight of the apparatus.

When the holding means is in the high grip state, the tool is held in asubstantially fixed spatial relationship with the workpiece, but atleast part of the tool (such as the drill bit, in the case where thetool is a drill) should be movable in order to perform its intendedfunction on the workpiece. The attractive force exerted by the holdingmeans in the high grip state must exceed that in the low grip state byan amount sufficient to exceed any forces likely to be generated by thetool when performing its function on the workpiece which would act toseparate the carriage from the workpiece surface.

In order to move the tool relative to the workpiece, the carriagepreferably comprises one or more elements held in frictional contactwith the workpiece surface by the holding means and adapted, when theholding means is in the low grip state, to move the carriage over theworkpiece surface.

The elements many comprise one or more wheels, with associatedconventional drive and steering mechanisms, or indeed any alternativearrangement capable of engaging with the workpiece surface in order tomove the carriage relative thereto, such as caterpiller tracks. Thefrictional arrangement between the elements may be adjusted in anyconventional manner so as to provide the optimum drive for the carriageconsist with the requirement not to cause damage to the workpiecesurface; the coefficient of friction between the element(s) and theworkpiece surface may be adjusted by providing tread patterns or suctioncups to the wheels/tracks, for example.

The holding means may comprise a vacuum system (suitably comprising ahigh flow, low pressure vacuum pump arranged to evacuate a plenumchamber adapted to seal against the workpiece surface) or amagnetic/electromagnetic system, according to the nature of theworkpiece; for most aerospace applications the workpiece would notnormally be ferromagnetic and therefore a vacuum system would be mostappropriate, however a magnetic system would be appropriate inapplications such as shipbuilding where large numbers of repeatoperations (such as drilling) need to be performed at differentlocations on ferromagnetic (frequently steel) workpieces.

The holding means and/or the carriage is/are preferably adapted toconform to the surface configuration of the workpiece immediatelyadjacent thereto when the holding means is in the low grip state.

Such an arrangement, whereby the apparatus conforms to the adjacentsurface of the workpiece as the apparatus moves thereover is necessarywhere the surface of the workpiece has a curved or complexconfiguration; it is also advantageous in assisting the holding means inensuring that the apparatus remains in contact with, and does notseparate from or fall off, the workpiece as the apparatus moves over itssurface. For a holding means operating on a vacuum principle, this maybe achieved by providing a brush type seal around the circumference ofthe vacuum plenum, where it abuts the workpiece surface. Conventionalsuspension units applied to the carriage would enable it to conform tothe workpiece surface configuration.

The holding means and/or the carriage may, additionally oralternatively, be adapted to conform to the surface configuration of theworkpiece immediately adjacent thereto when the holding means is in thehigh grip state.

When the holding means is switched to the high grip state, to ensurethat the apparatus is firmly clamped to the workpiece surface it isimportant that there be no movement of the holding means or the carriagewhich might affect the accuracy of the tool operation. In the case of avacuum system, the provision of a flexible rubber seal or the like wouldenhance the clamping of the apparatus to the workpiece in the high gripstate, as compared with a brush type seal, which would be more suitablefor clamping in the low grip state.

The apparatus preferably comprises means for sensing the position of thecarriage and/or the tool relative to the workpiece, and directing meansadapted to control the carriage in order to move the carriage over theworkpiece surface between pre-determined positions thereon.

Such a positioning arrangement facilitates the accurate positioning ofthe tool and reduces the time required to carry out repeated tooloperations by enabling the system to be operated with a minimum ofmanual intervention by an operator. This positioning arrangement ispreferably of the type comprising a radiation source for projecting animage onto the workpiece, surface, a radiation detector for detectingthe projected image, and processor means for calculating at leasttwo-dimensional co-ordinates of the projected image detected by theradiation detector relative to the tool, the directing means adapted tocontrol movement of the carriage so as to position the tool in apredefined spatial relationship with the projected image in response toa signal from the processor means.

The radiation source may be a laser. Advantageously the radiation sourceprovides radiation visible to the human eye so that an operator may viewthe image. The radiation source may be for example a Virtek Laseredge 3Dlaser protection system.

The radiation source may project an image in the form of an ellipse. Theradiation source may alternatively project an image in the form of across, or a circle. The image is preferably of a size in the range 0.5to 3.0 cm.

The image is projected onto a surface at a location where amanufacturing operation is to be carried out. Several images may beprojected simultaneously to provide, for example, a drill template on asurface such as an aircraft panel.

The radiation detector preferably comprises a camera and an imageprocessing system. The camera may comprise an array of solid statecharge coupled devices (CCDs). The array may be linear or rectangular.The CCDs produce a charge proportional to the amount of light falling onthem and the charge from each device in the array is preferably used bythe image processing system to build up an image.

The image processing system preferably comprises a frame grabber fordigitising the image and a computer adapted for processing the image.The image is advantageously processed by the computer to identifyfeatures such as areas of the same intensity or changes in intensity,for example. The image processor advantageously is thereby able toidentify an image, such as a cross, projected by the radiation source,and to locate the centre of the image.

There may also be provided means for sensing the position of the toolrelative to the workpiece surface and means for moving at least part ofthe tool relative to the carriage along at least two orthogonal axes.This will enable very accurate positioning of the tool relative to theworkpiece. The axes could be x and y axes coplanar with the adjacentsurface of the workpiece, and in particular that part of the workpiecesurface where the tool operation is to be performed. The moving meansmay comprise an electrical servo motor actuated moveable stage. A motioncontrol system could be used to control the electrical servos, withoptical encoders being used to provide positional feedback. The movingmeans may also be adapted to move the tool or part thereof along the zaxis.

In addition to accurately positioning the tool relative to the workpieceit will usually be necessary to ensure that the tool is oriented at thecorrect angle relative to the workpiece surface (for example, to ensurethat a drill bores perpendicularly through a curved plate). Accordingly,the apparatus may comprise means for sensing the angular orientation ofat least part of the tool relative to the workpiece surface and meansfor rotating at least part of the tool about at least one axis to adjustsaid angular orientation. Ideally, the arrangement would measure theangle of the tool (or, more usually, the tool bit) relative to theworkpiece surface, determine what movement is required about the x and yaxes (coplanar with the surface) is needed to bring the tool into thedesired angular orientation relative to the surface and then effectrotation in roll and/or pitch to achieve the desired orientation (whichin many cases will be with the tool bit normal to the surface).

The directing means is preferably adapted to control movement androtation effected by the moving means and the rotating means,respectively, such that the tool reaches a predetermined position and/ororientation relative to the surface of the workpiece, and to actuate thetool.

The apparatus may comprise a programmable controller adapted to controlthe directory means and to switch the holding means between the low andhigh grip states in order automatically to convey the carriage and toposition and orient the tool between predetermined locations andorientations relative to the workpiece surface, and to actuate the toolin order to carry out one or more predetermined tool operations on theworkpiece. Preferably the controller is programmable so as automaticallyto carry out different sequences of predetermined tool operations on aworkpiece and/or to carry out different sequences of predetermined tooloperations on a variety of different workpieces.

Such arrangements reduce the requirement for human intervention whilsttool operations are carried out, by making the process substantiallyautomated, and enable the use of several tool positioning apparatus on aworkpiece at one time, hence improving manufacturing productivity.

The invention will now be described by way of example and with referenceto the accompanying drawings, in which:

FIGS. 1 a and 1 b are schematic, partially cross-sectional front andside elevation views, respectively, of an embodiment of an apparatus inaccordance with the invention, and

FIG. 2 is a schematic diagram of the apparatus of FIGS. 1 a and 1 b inuse.

FIGS. 1 a and 1 b show a carriage 1 to which is mounted a tool 3 (adrill having a bit 5 is illustrated). The carriage 1 is substantiallycovered and surrounded by a vacuum cup 7, at least part 9 of which istransparent, for reasons to be described below. Around thecircumferential edge of the vacuum cup 7 is mounted a seal 11 in theform of a brush skirt and another seal 13 in the form of a rubber skirt;note that the brush skirt seal 11 is longer than, and therefore extendsfurther from the vacuum cup 7 than, rubber skirt seal 13. The brushskirt seal 11 and the rubber skirt seal 13 are preferably mounted so asto conform with the configuration of the surface upon which the carriagerests, in much the same manner as the carbon fibre “ground effectskirts” in use in Formula One motor racing some years ago—as will befurther described below.

Substantially enclosed within vacuum cup 7 are two pairs of wheels 15,at least one pair of which are driveable and/or steerable (asillustrated in FIG. 1 b, the right hand pair of wheels are driven andsteered by drive unit 17); wheels 15 have a rolling surface formed of anelastic compound, so as to provide good frictional engagement with thesurface the carriage rolls over, whilst preventing damage thereto.Wheels 15 are also provided with conventional suspension units 19 so asto allow each wheel to reciprocate independently in the verticaldirection of the drawings.

Around part of the drill 3 is a rotary, vacuum seal 21, which issealingly connected to vacuum cup 7 by a flexible diaphragm 23, soensuring that the vacuum cup 7 extends in substantially unbroken fashionover its entire surface area, whilst allowing drill 3 to move along 3orthogonal axes relative to vacuum cup 7 (and allowing drill bit 5 torotate about one of these axes). Moving means 25 which is rigidlymounted to the carriage 1 is adapted to move the drill 3 along thesethree axes, so as to move the drill 3 left and right as shown in thedrawing, into and out of the plane of the drawing, and up and down as inthe drawing.

A camera 27 is clamped to the drill 3 so as to move therewith, and isadjusted so as to receive an image of the end of the drill bit 5.Normalisation sensors 29 (only one is shown, in FIG. 1 b) are mounted tothe carriage 1 and are adapted so as to sense the angular orientation ofthe carriage 1, and particularly the drill bit 5, relative to thesurface on which the carriage 1 rests (not shown, for clarity) and intowhich a drilling operation is to be carried out. Rotating means 31 isrigidly mounted to the carriage 1 and is adapted to rotate the drill 3about two orthogonal axes substantially coplanar with the surface uponwhich the carriage rests, so as to ensure that the drill bit 5 is normalto the surface into which it is to drill, or so as to enable the drillbit 5 to drill at any desired angle other than normal into the surface.Control unit 33; which suitably comprises a microprocessor unit and acombined power source, powers and controls the operation of the drill 3,drive unit 17, moving means 25 and rotating means 33, as will be furtherdescribed below.

In use, carriage 1 is intended to move with a minimum of operatorintervention over the surface of a workpiece (not shown), so as to movethe tool 3 into an accurate position and orientation in order to carryout a precise manufacturing operation. In order to hold the carriage 1onto the surface of the workpiece and to prevent it from falling off asit moves around the workpiece, the interior of the vacuum cup 7 is atleast partially evacuated, forming a vacuum plenum, so that ambient airpressure holds the carriage 1 against the workpiece. The brush skirtseal 11 acts as the seal between the vacuum cup 7 and the workpiece, andis sufficiently flexible and/or flexibly mounted to conform to thesurface configuration of the workpiece. Nevertheless, as the seal 11 isessentially formed of a plurality of bristles which form an imperfectseal, so that ambient air can permeate the seal—in a controlledmanner—the force clamping the carriage 1 to the surface is not so greatas to prevent the wheels 15 from moving the carriage. Ideally, the brushskirt seal 11 and the low pressure within the vacuum cup 7 are designedso that, when the carriage needs to move, the net force clamping thecarriage 1 to the workpiece is not much more that the weight of thecarriage. When the carriage 1 is in approximately the correct position,the evacuation of the vacuum cup 7 is increased, compressing the brushskirt seal 11 and the suspension units 19 and bringing the rubber skirtseal 13 into contact with the surface of the workpiece. The rubber skirtseal 13 is similarly flexible and/or flexibly mounted as is the brushskirt seal 11, so as to confirm to the surface configuration of theworkpiece. However, the rubber skirt seal 13 is substantiallyimpermeable, so that the seal between the vacuum cup 7 and the surfaceof the workpiece is substantially airtight; as a result, the carriage 1is very firmly clamped to the workpiece. The low pressure within thevacuum cup 7 is controllable so as to ensure that the carriage 1 isunmoved by the forces, additional to its own weight, arising from thefine positioning of the tool 3 and, more particularly, from theoperation of the tool when drilling is taking place.

When the carriage 1 is clamped onto the workpiece, the tool 3 and thedrill bit 5 are accurately positioned and orientated by way of themoving means 25 and the rotating means 31, as will now be described withreference to FIG. 2, which illustrates the carriage 1 located on thesurface of an aircraft component 35, approximately in position for adrilling operation to be carried out and immediately before the carriage1 is firmly clamped to the component 35.

A laser projector 37 is positioned to project a beam of radiation 39onto the component 35 so as to project a cross shape which preciselydefines the position where a drilling operation is required. Because atleast the front portion 9 of the vacuum cup 7 is transparent, the crossis projected onto the surface of the component 35. The cross appearswithin the field of view of the camera 27, which then sends a signal tocontroller 41, indicating that the carriage 1 is approximatelypositioned.

On receipt of this signal, controller 41 sends signals halting the drivemeans 17 and to a high flow low pressure vacuum pump 43, so haltingmovement of carriage 1 and initiating the increased evacuation of vacuumcup 7 so as to clamp carriage 1 firmly to the component 35 (as describedabove).

Controller 41 then analyses the signal from camera 27 in order to assessthe precise location of the drill bit in relation to the laser crossprojected onto the component and signals control unit 33 to actuatemoving means 25 in order precisely to position the business end of thedrill bit 5 relative to the projected cross, which is precisely alignedon the spot where a drilling operation is required.

Controller 41 then interrogates normalisation sensors 29 (for clarity,no functional connection between controller 41 and normalisation sensor29 is depicted) to ascertain the angular orientation of the drill bit 5relative to the component surface; this measured orientation is comparedwith orientation data pre-programmed into controller 41 defining theprecise angular orientation of the desired drilling, and controller 41signals control unit 33 to actuate rotating means 31 in order preciselyto orientate the angle of the drill bit 5 relative to the surface to bedrilled.

Once the drill bit is accurately positioned and orientated, controller41 signals control unit 33 to initiate the drilling operation, byswitching the drill 3 on and moving the drill 3 along the axis of thedrill bit 5 as drilling occurs for a distance equal to the desireddrilling depth.

At any time, data may be input to the controller 41 by way of anoperation interface 45.

Now that a specific embodiment of the invention has been described,numerous modifications and variations will immediately spring to theminds of those skilled in the art. For example, the controller 41 andpump 43 may either be remote or affixed to the carriage 1 for greatercompactness (and the controller 41 and control unit 33 may comprise asingle integrated microprocessing unit); the interface 45 might comprisea keyboard and might also be located on the carriage 1, or it mightcomprise a remote infra-red or microwave linkage or the like.

The vacuum cup 7 depicted is in the form of a rectangular box—this couldbe of any shape provided it has a circumferential edge at least looselyconfigured so as to conform to the surface of the workpiece; it could,for example, be toroidal in shape with the manufacturing operation beingperformed through the central opening thereof, or it could comprise aplurality of small vacuum cups of any shape. The vacuum system describedcould be complemented by, or replaced with, any means capable ofproviding a variable attractive force, such as an electromagneticdevice, or even a system employing a releasable adhesive arrangement.

The illustrated embodiment incorporates a drill, for performing adrilling operation, however the drill could be replaced by any otherconventional tool for performing other manufacturing operations, oroperations such as welding, testing, painting, testing or otherlocalised treatment.

The laser projector 37 could be replaced by any comparable accuratepositioning arrangement, and the entire system could be automated so asto require a minimum of operator intervention.

1. Apparatus for positioning and holding a tool relative to a workpiece,said apparatus comprising: a carriage for conveying the tool over thesurface of the workpiece; and means for holding the carriage onto thesurface of the workpiece, the holding means selectively switchablebetween a low grip state and a high grip state, said low grip state iswhen the carriage is moveably held against the workpiece surface andsaid high grip state is when the carriage is fixedly held against theworkpiece surface for tool operation on said workpiece surface. 2.Apparatus according to claim 1 wherein the carriage comprises at leastone element held in frictional contact with the workpiece surface by theholding means and adapted, when the holding means is in the low gripstate, to move the carriage over the workpiece surface.
 3. Apparatusaccording to claim 1 wherein at least one of the holding means and thecarriage conforms to the surface of the workpiece immediately adjacentthereto when the holding means is in the low grip state.
 4. Apparatusaccording to claim 1 wherein at least one of the holding means and thecarriage conforms to the surface of the workpiece immediately adjacentthereto when the holding means is in the high grip state.
 5. Apparatusaccording to claim 1 further comprises: means for sensing the positionof at least one of the carriage and the tool relative to the workpiece,and directing means for moving the carriage over the workpiece surfacebetween predetermined positions thereon.
 6. Apparatus according to claim1 further comprising: means for sensing the position of the toolrelative to the workpiece surface; and means for moving at least part ofthe tool relative to the carriage along at least two orthogonal axes. 7.Apparatus according to claim 1 further comprising: means for sensing theangular orientation of at least part of the tool relative to theworkpiece surface and means for rotating at least part of the tool aboutat least one axis to adjust said angular orientation.
 8. Apparatus forpositioning and holding a tool relative to a workpiece, said apparatuscomprising: a carriage for conveying the tool over the surface of theworkpiece; means for holding the carriage onto the surface of theworkpiece, the holding means selectively switchable between a low gripstate and a high grip state, said low grip state is when the carriage ismoveable held against the workpiece surface and said high grip state iswhen the carriage is fixedly held against the workpiece surface for tooloperation on said workpiece surface; means for sensing the position ofthe carriage relative to the workpiece; directing means for moving thecarriage over the workpiece surface between predetermined positionsthereon; means for sensing the position of the tool relative to theworkpiece surface; and tool moving means for moving at least part of thetool relative to the carriage along at least two orthogonal axes,wherein the directing means controls said tool moving means to move saidtool to at least one of a predetermined position and orientationrelative to the surface of the workpiece, and actuates the tool. 9.Apparatus for positioning and holding a tool relative to a workpiece,said apparatus comprising: a carriage for conveying the tool over thesurface of the workpiece; means for holding the carriage onto thesurface of the workpiece, the holding means selectively switchablebetween a low grip state and a high grip state, said low grip state iswhen the carriage is moveable held against the workpiece surface andsaid high grip state is when the carriage is fixedly held against theworkpiece surface for tool operation on said workpiece surface; meansfor sensing the position of the carriage relative to the workpiece;directing means for moving the carriage over the workpiece surfacebetween predetermined positions thereon, means for sensing the angularorientation of at least part of the tool relative to the workpiecesurface; and tool moving means for rotating at least part of the toolabout at least one axis to adjust said angular orientation, wherein thedirecting means controls said tool moving means to move said tool to atleast one of a predetermined position and orientation relative to thesurface of the workpiece, and actuates the tool.
 10. Apparatus accordingto claim 8 further including a programmable controller for controllingthe directing means and for switching the holding means between the lowand high grip states in order automatically to move the carriage and toposition and orient the tool between predetermined locations andorientations relative to the workpiece surface, and for actuating thetool in order to carry out at least one predetermined tool operation onthe workpiece.
 11. Apparatus according to claim 10 wherein thecontroller is programmable so as automatically to carry out differentsequences of predetermined tool operations on a workpiece.
 12. Apparatusaccording to claim 10 wherein the controller is programmable so asautomatically to carry out different sequences of predetermined tooloperations on a variety of different workpieces.
 13. Apparatus accordingto claim 9 further including a programmable controller for controllingthe directing means and for switching the holding means between the lowand high grip states in order automatically to move the carriage and toposition and orient the tool between predetermined locations andorientations relative to the workpiece surface, and for actuating thetool in order to carry out at least one predetermined tool operation onthe workpiece.
 14. Apparatus according to claim 13 wherein thecontroller is programmable so as automatically to carry out differentsequences of predetermined tool operations on a workpiece.
 15. Apparatusaccording to claim 14 wherein the controller is programmable so asautomatically to carry out different sequences of predetermined tooloperations on a variety of different workpieces.
 16. Apparatus accordingto claim 2 wherein at least one of the holding means and the carriageconforms to the surface of the workpiece immediately adjacent theretowhen the holding means is in the low grip state.
 17. Apparatus accordingto claim 2 wherein at least one of the holding means and the carriageconforms to the surface of the workpiece immediately adjacent theretowhen the holding means is in the high grip state.
 18. Apparatusaccording to claim 2 further comprising: means for sensing the positionof at least one of the carriage and the tool relative to the workpiece;and directing means for moving the carriage over the workpiece surfacebetween predetermined positions thereon.
 19. Apparatus according toclaim 2 further comprising: means for sensing the position of the toolrelative to the workpiece surface; and means for moving at least part ofthe tool relative to the carriage along at least two orthogonal axes.20. Apparatus according to claim 2 further comprising: means for sensingthe angular orientation of at least part of the tool relative to theworkpiece surface; and means for rotating at least part of the toolabout at least one axis to adjust said angular orientation.